Fiber swelling to improve cycle performance of paper-based separator for lithium-ion batteries application

It is well established that paper-based separators display short-circuit risk in lithium-ion batteries due to their intrinsic micron-sized pores. In this research, we have adjusted pore structure of paper by fiber swelling in liquid electrolyte. Specifically, the paper-based separator is prepared by propionylated sisal fibers through a wet papermaking process. Scanning electron microscope (SEM) and multi-range X-ray nano-computed tomography (CT) images display strong swelling of modified fibers after electrolyte absorption, which can effectively decrease the pore size of separator. Due to the high electrolyte uptake (817 wt%), paper-based separator exhibits ionic conductivity of 2.93 mS cm−1. 7Li solid-state NMR spectroscopy and Gaussian simulation reveal that the formation of local high Li+ ion concentration in the separator and its low absorption energy with Li+ ion (62.2 kcal mol−1) is conducive to the ionic transportation. In particular, the assembled Li/separator/LiFePO4 cell displays wide electrochemical stability window (5.2 V) and excellent cycle performance (capacity retention of 96.6% after 100 cycles at 0.5 C) due to the reduced side reactions as well as enhanced electrolyte absorption and retention capacity by propionylation. Our proposed strategy will provide a novel perspective to design high-performance bio-based separators to boost the development of clean and sustainable energy economy.